block/nfs: do not poll within a coroutine

block/nfs: do not poll within a coroutine

Since the former nfs_get_allocated_file_size is now a coroutine
function, it must suspend rather than poll.  Switch BDRV_POLL_WHILE()
to a qemu_coroutine_yield() loop and schedule nfs_co_generic_bh_cb()
in place of the call to bdrv_wakeup().

Fixes: 82618d7bc341 ("block: Convert bdrv_get_allocated_file_size() to co_wrapper", 2023-02-01)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230412112606.80983-1-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>